A MATLAB®-based postprocessor for Multi-Blade Coordinate transformation of wind turbine state-space models
by Gungit Bir, NREL
MBC is a set of MatLab scripts that performs multi-blade coordinate transformation (MBC) on wind turbine system models. The dynamics of wind turbine rotor blades are conventionally expressed in rotating frames attached to the individual blades. The tower-nacelle subsystem sees the combined effect of all rotor blades, not the individual blades. This is because the rotor responds as a whole to excitations such as aerodynamic gusts, control inputs, and tower-nacelle motion—all of which occur in a nonrotating frame. MBC helps integrate the dynamics of individual blades and express them in a fixed (nonrotating) frame.
MBC is mandatory to controls and stability analyses—erroneous predictions can result otherwise. A novel feature of this MBC code is that it can handle variable-speed operation and turbines with dissimilar blades. Depending on the analysis objective, a user may generate system models either in the first-order (state-space) form or the second-order (physical-domain) form. MBC3 can handle both types of system models. Key advantages of MBC are: capturing cumulative dynamics of the rotor blades and its interaction with the tower-nacelle subsystem, well-conditioning of system matrices by eliminating non-essential periodicity, and filtering operation.